1. Field of the Invention
The present invention relates to locking devices for screw heads, and in particular relates to means for separating the locking devices from the screw heads to permit removal of the screw.
2. Description of the Prior Art
Guide tubes are secured to the upper support plate in the upper internals of a nuclear reactor by a plurality of cap screws. These screws, after being torqued, are prevented from working loose by a locking cup, which also prevents the screw head from floating free in the event of breakage of the screw shaft. The locking cup includes a cylindrical side wall which coaxially encircles the screw head and has at its lower end a radially outwardly extending annular flange welded to the guide tube. In one type of locking cup, the upper end of the side wall is crimped or deformed into a plurality of equiangularly spaced flutes in the head of the cap screw to provide a connection between the locking cup and the screw. Another type of locking cup is provided with a radially inwardly extending annular flange or end wall at the upper end of the cylindrical side wall which partially covers the top or outer surface of the cap screw. The inner edge of this flange is welded to the cap screw.
With the first or fluted type of locking cup, the cap screw can be removed by simply untorquing it, which forces the deformed portions of the locking cup side wall back out of the flutes. The locking cup side wall can then be reshaped and reused with a new screw. In the second type of locking cup, however, simple untorquing of the cap screw results in breakage of the locking cup, with part remaining attached to the screw head and part remaining attached to the guide tube. The part remaining attached to the guide tube is not reusable and the locking cup may break up into a number of parts, resulting in loose debris. Normal replacement of the locking cups, which requires welding, is impractical because the work must be done remotely underwater to protect workers from exposure to radiation from the guide tubes. Accordingly, an effective method and apparatus for removing cap screws with this second type of locking cup is needed.